目录
创建SqlSession
public static void main(String[] args) throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
Employee employeeMapper = sqlSession.getMapper(Employee.class);
List<Employee> all = employeeMapper.getAll();
for (Employee item : all)
System.out.println(item);
} finally {
sqlSession.close();
}
}
//DefaultSqlSessionFactory
public SqlSession openSession() {
return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, false);
}
/**
* ExecutorType 指定Executor的类型，分为三种：SIMPLE, REUSE, BATCH，默认使用的是SIMPLE
* TransactionIsolationLevel 指定事务隔离级别，使用null,则表示使用数据库默认的事务隔离界别
* autoCommit 是否自动提交，传过来的参数为false，表示不自动提交
*/
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
// 获取配置中的环境信息，包括了数据源信息、事务等
final Environment environment = configuration.getEnvironment();
// 创建事务工厂
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
// 创建事务，配置事务属性
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
// 创建Executor，即执行器
// 它是真正用来Java和数据库交互操作的类，后面会展开说。
final Executor executor = configuration.newExecutor(tx, execType);//入口
// 创建DefaultSqlSession对象返回，其实现了SqlSession接口
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx);
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
//Configuration
//创建一个执行器，默认是SIMPLE
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
//根据executorType来创建相应的执行器,Configuration默认是SIMPLE
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
//创建SimpleExecutor实例，并且包含Configuration和transaction属性
executor = new SimpleExecutor(this, transaction);
}
//如果要求缓存，生成另一种CachingExecutor,装饰者模式,默认都是返回CachingExecutor
/**
* 二级缓存开关配置示例
* <settings>
* <setting name="cacheEnabled" value="true"/>
* </settings>
*/
if (cacheEnabled) {
//CachingExecutor使用装饰器模式，将executor的功能添加上了二级缓存的功能，二级缓存会单独文章来讲
executor = new CachingExecutor(executor);
}
//此处调用插件,通过插件可以改变Executor行为，此处我们后面单独文章讲
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
- 从configuration获取Environment对象，从Environment获取TransactionFactory，创建Transaction，默认是JdbcTransaction
- 创建Executor。如果开启二级缓存会创建CachingExecutor，CachingExecutor通过装饰者模式给执行器添加缓存功能。Executor支持三种：
- SimpleExecutor：默认的，根据对应的sql直接执行，每执行一次update或select，就开启一个Statement对象，用完立刻关闭Statement对象
- BatchExecutor：执行update（没有select，JDBC批处理不支持select），将所有sql都添加到批处理中，等待统一执行，它缓存了多个Statement对象，每个Statement对象都是addBatch()完毕后，等待逐一执行executeBatch()批处理的；BatchExecutor相当于维护了多个桶，每个桶里都装了很多属于自己的SQL，就像苹果蓝里装了很多苹果，番茄蓝里装了很多番茄，最后，再统一倒进仓库。
- ReuseExecutor：可重用的执行器，重用的对象是Statement，也就是说该执行器会缓存同一个sql的Statement，省去Statement的重新创建，优化性能。内部的实现是通过一个HashMap来维护Statement对象的。由于当前Map只在该session中有效，所以使用完成后记得调用flushStatements来清除Map。
- 创建DefaultSqlSession对象
创建Mapper代理类
//DefaultSqlSessionFactory
public <T> T getMapper(Class<T> type) {
return this.configuration.getMapper(type, this);
}
//Configuration
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return this.mapperRegistry.getMapper(type, sqlSession);
}
//MapperRegistry
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
//获取代理类工厂
MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
} else {
try {
//通过反射返回一个代理对象
//入口
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception var5) {
throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
}
}
}
public T newInstance(SqlSession sqlSession) {
MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
return this.newInstance(mapperProxy);
}
- knowMappers中获取代理工厂
通过代理类执行sql
对目标方法的拦截执行在自定义拦截器MapperProxy的invoke方法。
public class MapperProxy<T> implements InvocationHandler, Serializable {
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 如果方法是定义在 Object 类中的，则直接调用
if (Object.class.equals(method.getDeclaringClass())) {
try {
return method.invoke(this, args);
} catch (Throwable var5) {
throw ExceptionUtil.unwrapThrowable(var5);
}
} else {
// 从缓存中获取 MapperMethod 对象，若缓存未命中，则创建 MapperMethod 对象
MapperMethod mapperMethod = this.cachedMapperMethod(method);//入口1
// 调用 execute 方法执行 SQL
return mapperMethod.execute(this.sqlSession, args);//入口2
}
}
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);
if (mapperMethod == null) {
//创建一个MapperMethod，参数为mapperInterface和method还有Configuration
mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());
this.methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
}
//MapperMethod
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
// 根据 SQL 类型执行相应的数据库操作
switch (command.getType()) {
case INSERT: {
// 对用户传入的参数进行转换，下同
Object param = method.convertArgsToSqlCommandParam(args);
// 执行插入操作，rowCountResult 方法用于处理返回值
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
// 执行更新操作
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
// 执行删除操作
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
// 根据目标方法的返回类型进行相应的查询操作
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
// 执行查询操作，并返回多个结果
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
// 执行查询操作，并将结果封装在 Map 中返回
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
// 执行查询操作，并返回一个 Cursor 对象
result = executeForCursor(sqlSession, args);
} else {
Object param = method.convertArgsToSqlCommandParam(args);
// 执行查询操作，并返回一个结果
result = sqlSession.selectOne(command.getName(), param);
}
break;
case FLUSH:
// 执行刷新操作
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
return result;
}
- 检测被拦截的方法是不是定义在 Object 中的，比如 equals、hashCode 方法等。对于这类方法，直接执行即可
- 如果sql类型是：
- INSERT：先通过convertArgsToSqlCommandParam方法处理参数，然后通过sqlSession执行insert，最后通过rowCountResult对结果转换处理
- UPDATE：先通过convertArgsToSqlCommandParam方法处理参数，然后通过sqlSession执行update，最后通过rowCountResult对结果转换处理
- DELETE: 先通过convertArgsToSqlCommandParam方法处理参数，然后通过sqlSession执行delete，最后通过rowCountResult对结果转换处理
- SELECT:
- 如果无返回值或者hasResultHandler
- 有多个返回值
- 返回的是map
- 返回Cursor
- 返回一个结果：先通过convertArgsToSqlCommandParam方法处理参数，然后通过sqlSession执行selectOne
INSERT
UPDATE
DELETE
SELECT
如果无返回值或者hasResultHandler
有多个返回值
返回一个结果
//DefaultSqlSession
public <T> T selectOne(String statement, Object parameter) {
// 调用 selectList 获取结果
List<T> list = this.<T>selectList(statement, parameter);//入口
if (list.size() == 1) {
// 返回结果
return list.get(0);
} else if (list.size() > 1) {
// 如果查询结果大于1则抛出异常
throw new TooManyResultsException(
"Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
} else {
return null;
}
}
private final Executor executor;
public <E> List<E> selectList(String statement, Object parameter) {
// 调用重载方法
return this.selectList(statement, parameter, RowBounds.DEFAULT);
}
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 通过MappedStatement的Id获取 MappedStatement
MappedStatement ms = configuration.getMappedStatement(statement);
// 调用 Executor 实现类中的 query 方法
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
//CachingExecutor
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
// 获取 BoundSql
//入口
BoundSql boundSql = ms.getBoundSql(parameterObject);
// 创建 CacheKey
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
// 调用重载方法
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
创建BoundSql对象
//MappedStatement
public BoundSql getBoundSql(Object parameterObject) {
BoundSql boundSql = this.sqlSource.getBoundSql(parameterObject);//入口
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings == null || parameterMappings.isEmpty()) {
boundSql = new BoundSql(this.configuration, boundSql.getSql(), this.parameterMap.getParameterMappings(), parameterObject);
}
Iterator var4 = boundSql.getParameterMappings().iterator();
while(var4.hasNext()) {
ParameterMapping pm = (ParameterMapping)var4.next();
String rmId = pm.getResultMapId();
if (rmId != null) {
ResultMap rm = this.configuration.getResultMap(rmId);
if (rm != null) {
this.hasNestedResultMaps |= rm.hasNestedResultMaps();
}
}
}
return boundSql;
}
//DynamicSqlSource
public BoundSql getBoundSql(Object parameterObject) {
// 创建 DynamicContext
DynamicContext context = new DynamicContext(configuration, parameterObject);
// 解析 SQL 片段，并将解析结果存储到 DynamicContext 中，这里会将${}替换成method对应的运行时参数，也会解析<if><where>等SqlNode
rootSqlNode.apply(context);
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
/*
* 构建 StaticSqlSource，在此过程中将 sql 语句中的占位符 #{} 替换为问号 ?，
* 并为每个占位符构建相应的 ParameterMapping
*/
SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());//入口
// 调用 StaticSqlSource 的 getBoundSql 获取 BoundSql
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
// 将 DynamicContext 的 ContextMap 中的内容拷贝到 BoundSql 中
for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
}
return boundSql;
}
//SqlSourceBuilder
public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
// 创建 #{} 占位符处理器
ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
// 创建 #{} 占位符解析器
GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
// 解析 #{} 占位符，并返回解析结果字符串
String sql = parser.parse(originalSql);//入口
// 封装解析结果到 StaticSqlSource 中，并返回,因为所有的动态参数都已经解析了，可以封装成一个静态的SqlSource
return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
}
public String parse(String text) {
if (text != null && !text.isEmpty()) {
char[] src = text.toCharArray();
int offset = 0;
int start = text.indexOf(this.openToken, offset);
if (start == -1) {
return text;
} else {
StringBuilder builder = new StringBuilder();
for(StringBuilder expression = null; start > -1; start = text.indexOf(this.openToken, offset)) {
if (start > 0 && src[start - 1] == '\') {
builder.append(src, offset, start - offset - 1).append(this.openToken);
offset = start + this.openToken.length();
} else {
if (expression == null) {
expression = new StringBuilder();
} else {
expression.setLength(0);
}
builder.append(src, offset, start - offset);
offset = start + this.openToken.length();
int end;
for(end = text.indexOf(this.closeToken, offset); end > -1; end = text.indexOf(this.closeToken, offset)) {
if (end <= offset || src[end - 1] != '\') {
expression.append(src, offset, end - offset);
int var10000 = end + this.closeToken.length();
break;
}
expression.append(src, offset, end - offset - 1).append(this.closeToken);
offset = end + this.closeToken.length();
}
if (end == -1) {
builder.append(src, start, src.length - start);
offset = src.length;
} else {
builder.append(this.handler.handleToken(expression.toString()));//入口
offset = end + this.closeToken.length();
}
}
}
if (offset < src.length) {
builder.append(src, offset, src.length - offset);
}
return builder.toString();
}
} else {
return "";
}
}
public String handleToken(String content) {
// 获取 content 的对应的 ParameterMapping
parameterMappings.add(buildParameterMapping(content));//入口
// 返回 ?
return "?";
}
private ParameterMapping buildParameterMapping(String content) {
/*
* 将#{xxx} 占位符中的内容解析成 Map。
* #{age,javaType=int,jdbcType=NUMERIC,typeHandler=MyTypeHandler}
* 上面占位符中的内容最终会被解析成如下的结果：
* {
* "property": "age",
* "typeHandler": "MyTypeHandler",
* "jdbcType": "NUMERIC",
* "javaType": "int"
* }
*/
Map<String, String> propertiesMap = parseParameterMapping(content);
String property = propertiesMap.get("property");
Class<?> propertyType;
// metaParameters 为 DynamicContext 成员变量 bindings 的元信息对象
if (metaParameters.hasGetter(property)) {
propertyType = metaParameters.getGetterType(property);
/*
* parameterType 是运行时参数的类型。如果用户传入的是单个参数，比如 Employe 对象，此时
* parameterType 为 Employe.class。如果用户传入的多个参数，比如 [id = 1, author = "chenhao"]，
* MyBatis 会使用 ParamMap 封装这些参数，此时 parameterType 为 ParamMap.class。
*/
} else if (typeHandlerRegistry.hasTypeHandler(parameterType)) {
propertyType = parameterType;
} else if (JdbcType.CURSOR.name().equals(propertiesMap.get("jdbcType"))) {
propertyType = java.sql.ResultSet.class;
} else if (property == null || Map.class.isAssignableFrom(parameterType)) {
propertyType = Object.class;
} else {
/*
* 代码逻辑走到此分支中，表明 parameterType 是一个自定义的类，
* 比如 Employe，此时为该类创建一个元信息对象
*/
MetaClass metaClass = MetaClass.forClass(parameterType, configuration.getReflectorFactory());
// 检测参数对象有没有与 property 想对应的 getter 方法
if (metaClass.hasGetter(property)) {
// 获取成员变量的类型
propertyType = metaClass.getGetterType(property);
} else {
propertyType = Object.class;
}
}
ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType);
// 将 propertyType 赋值给 javaType
Class<?> javaType = propertyType;
String typeHandlerAlias = null;
// 遍历 propertiesMap
for (Map.Entry<String, String> entry : propertiesMap.entrySet()) {
String name = entry.getKey();
String value = entry.getValue();
if ("javaType".equals(name)) {
// 如果用户明确配置了 javaType，则以用户的配置为准
javaType = resolveClass(value);
builder.javaType(javaType);
} else if ("jdbcType".equals(name)) {
// 解析 jdbcType
builder.jdbcType(resolveJdbcType(value));
} else if ("mode".equals(name)) {...}
else if ("numericScale".equals(name)) {...}
else if ("resultMap".equals(name)) {...}
else if ("typeHandler".equals(name)) {
typeHandlerAlias = value;
}
else if ("jdbcTypeName".equals(name)) {...}
else if ("property".equals(name)) {...}
else if ("expression".equals(name)) {
throw new BuilderException("Expression based parameters are not supported yet");
} else {
throw new BuilderException("An invalid property '" + name + "' was found in mapping #{" + content
+ "}. Valid properties are " + parameterProperties);
}
}
if (typeHandlerAlias != null) {
builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias));
}
// 构建 ParameterMapping 对象
return builder.build();
}
- 从configuration中获取MappedStatement
- 将数据从MappedStatement转换到BoundSql
- 调用Executor的query方法
Executor.query
//CachingExecutor
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
// 从 MappedStatement 中获取缓存
Cache cache = ms.getCache();
// 若映射文件中未配置缓存或参照缓存，此时 cache = null
if (cache != null) {
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
// 若缓存未命中，则调用被装饰类的 query 方法，也就是SimpleExecutor的query方法
list = delegate.<E>query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
// 调用被装饰类的 query 方法,这里的delegate我们知道应该是SimpleExecutor
return delegate.<E>query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
//BaseExecutor
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
if (closed) {
throw new ExecutorException("Executor was closed.");
}
if (queryStack == 0 && ms.isFlushCacheRequired()) {
clearLocalCache();
}
List<E> list;
try {
queryStack++;
// 从一级缓存中获取缓存项，一级缓存我们也下一篇文章单独讲
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// 一级缓存未命中，则从数据库中查询
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
clearLocalCache();
}
}
return list;
}
//BaseExecutor
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds,
ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
// 向缓存中存储一个占位符
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 调用 doQuery 进行查询
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);//入口
} finally {
// 移除占位符
localCache.removeObject(key);
}
// 缓存查询结果
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
//SimpleExecutor
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
// 创建 StatementHandler
//入口1
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
// 创建 Statement
//入口2
stmt = prepareStatement(handler, ms.getStatementLog());
// 执行查询操作
return handler.query(stmt, resultHandler);
} finally {
// 关闭 Statement
closeStatement(stmt);
}
}
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement,
Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
// 创建具有路由功能的 StatementHandler
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
// 应用插件到 StatementHandler 上
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
// 获取数据库连接
Connection connection = getConnection(statementLog);
// 创建 Statement，
stmt = handler.prepare(connection, transaction.getTimeout());
// 为 Statement 设置参数
handler.parameterize(stmt);
return stmt;
}
- 先从一级缓存查询，没查询到从二级缓存查询，如果还为查询到则从数据库查询
- 创建RoutingStatementHandler
- 创建prepareStatement
- 通过RoutingStatementHandler执行query
创建prepareStatement
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
Statement statement = null;
try {
// 创建 Statement
statement = instantiateStatement(connection);//入口
// 设置超时和 FetchSize
setStatementTimeout(statement, transactionTimeout);
setFetchSize(statement);
return statement;
} catch (SQLException e) {
closeStatement(statement);
throw e;
} catch (Exception e) {
closeStatement(statement);
throw new ExecutorException("Error preparing statement. Cause: " + e, e);
}
}
protected Statement instantiateStatement(Connection connection) throws SQLException {
//获取sql字符串，比如"select * from user where id= ?"
String sql = boundSql.getSql();
// 根据条件调用不同的 prepareStatement 方法创建 PreparedStatement
if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
String[] keyColumnNames = mappedStatement.getKeyColumns();
if (keyColumnNames == null) {
//通过connection获取Statement，将sql语句传进去
return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
} else {
return connection.prepareStatement(sql, keyColumnNames);//入口
}
} else if (mappedStatement.getResultSetType() != null) {
return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
} else {
return connection.prepareStatement(sql);
}
}
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
boolean canServerPrepare = true;
String nativeSql = getProcessEscapeCodesForPrepStmts() ? nativeSQL(sql) : sql;
if (this.useServerPreparedStmts && getEmulateUnsupportedPstmts()) {
canServerPrepare = canHandleAsServerPreparedStatement(nativeSql);
}
if (this.useServerPreparedStmts && getEmulateUnsupportedPstmts()) {
canServerPrepare = canHandleAsServerPreparedStatement(nativeSql);
}
if (this.useServerPreparedStmts && canServerPrepare) {
if (this.getCachePreparedStatements()) {
......
} else {
try {
//这里使用的是ServerPreparedStatement创建PreparedStatement
pStmt = ServerPreparedStatement.getInstance(getMultiHostSafeProxy(), nativeSql, this.database, resultSetType, resultSetConcurrency);
pStmt.setResultSetType(resultSetType);
pStmt.setResultSetConcurrency(resultSetConcurrency);
} catch (SQLException sqlEx) {
// Punt, if necessary
if (getEmulateUnsupportedPstmts()) {
pStmt = (PreparedStatement) clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
} else {
throw sqlEx;
}
}
}
} else {
pStmt = (PreparedStatement) clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
}
public class ServerPreparedStatement extends PreparedStatement {
//存放运行时参数的数组
private ServerPreparedStatement.BindValue[] parameterBindings;
//服务器预编译好的sql语句返回的serverStatementId
private long serverStatementId;
private void serverPrepare(String sql) throws SQLException {
synchronized(this.connection.getMutex()) {
MysqlIO mysql = this.connection.getIO();
try {
//向sql服务器发送了一条PREPARE指令
Buffer prepareResultPacket = mysql.sendCommand(MysqlDefs.COM_PREPARE, sql, (Buffer)null, false, characterEncoding, 0);
//记录下了预编译好的sql语句所对应的serverStatementId
this.serverStatementId = prepareResultPacket.readLong();
this.fieldCount = prepareResultPacket.readInt();
//获取参数个数，比喻 select * from user where id= ？and name = ？，其中有两个？，则这里返回的参数个数应该为2
this.parameterCount = prepareResultPacket.readInt();
this.parameterBindings = new ServerPreparedStatement.BindValue[this.parameterCount];
for(int i = 0; i < this.parameterCount; ++i) {
//根据参数个数，初始化数组
this.parameterBindings[i] = new ServerPreparedStatement.BindValue();
}
} catch (SQLException var16) {
throw sqlEx;
} finally {
this.connection.getIO().clearInputStream();
}
}
}
}
- 最终是通过ServerPreparedStatement来创建PreparedStatement的
ServerPreparedStatement初始化的时候就向sql服务器发送了一条PREPARE指令，把SQL语句传到mysql服务器，如select * from user where id= ？and name = ？，mysql服务器会对sql进行编译，并保存在服务器，返回预编译语句对应的id，并保存在ServerPreparedStatement中，同时创建BindValue[] parameterBindings数组，后面设置参数就直接添加到此数组中。
将运行时参数设置到PreparedStatement
//
public void parameterize(Statement statement) throws SQLException {
// 通过参数处理器 ParameterHandler 设置运行时参数到 PreparedStatement 中
parameterHandler.setParameters((PreparedStatement) statement);
}
public class DefaultParameterHandler implements ParameterHandler {
private final TypeHandlerRegistry typeHandlerRegistry;
private final MappedStatement mappedStatement;
private final Object parameterObject;
private final BoundSql boundSql;
private final Configuration configuration;
public void setParameters(PreparedStatement ps) {
/*
* 从 BoundSql 中获取 ParameterMapping 列表，每个 ParameterMapping 与原始 SQL 中的 #{xxx} 占位符一一对应
*/
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
// 获取属性名
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) {
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
// 为用户传入的参数 parameterObject 创建元信息对象
MetaObject metaObject = configuration.newMetaObject(parameterObject);
// 从用户传入的参数中获取 propertyName 对应的值
value = metaObject.getValue(propertyName);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
// 由类型处理器 typeHandler 向 ParameterHandler 设置参数
typeHandler.setParameter(ps, i + 1, value, jdbcType);//入口
} catch (TypeException e) {
throw new TypeException(...);
} catch (SQLException e) {
throw new TypeException(...);
}
}
}
}
}
}
- 首先从boundSql中获取parameterMappings 集合，然后遍历获取 parameterMapping中的propertyName ，如#{name} 中的name,然后从运行时参数parameterObject中获取name对应的参数值，最后设置到PreparedStatement 中，我们主要来看是如何设置参数的。
typeHandler.setParameter(ps, i + 1, value, jdbcType);，这句代码最终会向我们例子中一样执行，如下
//
public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, parameter);
}
还记得我们的PreparedStatement是什么吗？是ServerPreparedStatement，那我们就来看看ServerPreparedStatement的setString方法
//
public void setString(int parameterIndex, String x) throws SQLException {
this.checkClosed();
if (x == null) {
this.setNull(parameterIndex, 1);
} else {
//根据参数下标从parameterBindings数组总获取BindValue
ServerPreparedStatement.BindValue binding = this.getBinding(parameterIndex, false);
this.setType(binding, this.stringTypeCode);
//设置参数值
binding.value = x;
binding.isNull = false;
binding.isLongData = false;
}
}
protected ServerPreparedStatement.BindValue getBinding(int parameterIndex, boolean forLongData) throws SQLException {
this.checkClosed();
if (this.parameterBindings.length == 0) {
throw SQLError.createSQLException(Messages.getString("ServerPreparedStatement.8"), "S1009", this.getExceptionInterceptor());
} else {
--parameterIndex;
if (parameterIndex >= 0 && parameterIndex < this.parameterBindings.length) {
if (this.parameterBindings[parameterIndex] == null) {
this.parameterBindings[parameterIndex] = new ServerPreparedStatement.BindValue();
} else if (this.parameterBindings[parameterIndex].isLongData && !forLongData) {
this.detectedLongParameterSwitch = true;
}
this.parameterBindings[parameterIndex].isSet = true;
this.parameterBindings[parameterIndex].boundBeforeExecutionNum = (long)this.numberOfExecutions;
//根据参数下标从parameterBindings数组总获取BindValue
return this.parameterBindings[parameterIndex];
} else {
throw SQLError.createSQLException(Messages.getString("ServerPreparedStatement.9") + (parameterIndex + 1) + Messages.getString("ServerPreparedStatement.10") + this.parameterBindings.length, "S1009", this.getExceptionInterceptor());
}
}
}
就是根据参数下标从ServerPreparedStatement的参数数组parameterBindings中获取BindValue对象，然后设置值，好了现在ServerPreparedStatement包含了预编译SQL语句的Id和参数数组，最后一步便是执行SQL了。
RoutingStatementHandler.query
//
return handler.<E>query(stmt, resultHandler);
我们来看看query是怎么做的
//
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement)statement;
//直接执行ServerPreparedStatement的execute方法
ps.execute();
return this.resultSetHandler.handleResultSets(ps);
}
public boolean execute() throws SQLException {
this.checkClosed();
ConnectionImpl locallyScopedConn = this.connection;
if (!this.checkReadOnlySafeStatement()) {
throw SQLError.createSQLException(Messages.getString("PreparedStatement.20") + Messages.getString("PreparedStatement.21"), "S1009", this.getExceptionInterceptor());
} else {
ResultSetInternalMethods rs = null;
CachedResultSetMetaData cachedMetadata = null;
synchronized(locallyScopedConn.getMutex()) {
//略....
rs = this.executeInternal(rowLimit, sendPacket, doStreaming, this.firstCharOfStmt == 'S', metadataFromCache, false);
//略....
}
return rs != null && rs.reallyResult();
}
}
省略了很多代码，只看最关键的executeInternal
//ServerPreparedStatement
protected ResultSetInternalMethods executeInternal(int maxRowsToRetrieve, Buffer sendPacket, boolean createStreamingResultSet, boolean queryIsSelectOnly, Field[] metadataFromCache, boolean isBatch) throws SQLException {
try {
return this.serverExecute(maxRowsToRetrieve, createStreamingResultSet, metadataFromCache);
} catch (SQLException var11) {
throw sqlEx;
}
}
private ResultSetInternalMethods serverExecute(int maxRowsToRetrieve, boolean createStreamingResultSet, Field[] metadataFromCache) throws SQLException {
synchronized(this.connection.getMutex()) {
//略....
MysqlIO mysql = this.connection.getIO();
Buffer packet = mysql.getSharedSendPacket();
packet.clear();
packet.writeByte((byte)MysqlDefs.COM_EXECUTE);
//将该语句对应的id写入数据包
packet.writeLong(this.serverStatementId);
int i;
//将对应的参数写入数据包
for(i = 0; i < this.parameterCount; ++i) {
if (!this.parameterBindings[i].isLongData) {
if (!this.parameterBindings[i].isNull) {
this.storeBinding(packet, this.parameterBindings[i], mysql);
} else {
nullBitsBuffer[i / 8] = (byte)(nullBitsBuffer[i / 8] | 1 << (i & 7));
}
}
}
//发送数据包,表示执行id对应的预编译sql
Buffer resultPacket = mysql.sendCommand(MysqlDefs.COM_EXECUTE, (String)null, packet, false, (String)null, 0);
//略....
ResultSetImpl rs = mysql.readAllResults(this, this.resultSetType, resultPacket, true, (long)this.fieldCount, metadataFromCache);
//返回结果
return rs;
}
}
ServerPreparedStatement在记录下serverStatementId后，对于相同SQL模板的操作，每次只是发送serverStatementId和对应的参数，省去了编译sql的过程。 至此我们的已经从数据库拿到了查询结果。